Piston compressor

ABSTRACT

A piston compressor includes first and second cylinder blocks having an inlet port and a swash plate chamber, a drive shaft having first and second guide holes, and a swash plate having first and second supply ports. The swash plate chamber communicates with the inlet port and also with the first and second guide holes via the first and second supply ports, respectively. A distance from the inlet port to the first supply port when the first supply port is moved closest to the inlet port is greater than a distance from the inlet port to the second supply port when the second supply port is moved closest to the inlet port, and the smallest flow passage area in the first supply port and the first guide hole is greater than the smallest flow passage area in the second supply port and the second guide hole.

BACKGROUND OF THE INVENTION

The present invention relates to a piston compressor.

Japanese Utility Model Application Publication No. 63-174579 discloses apiston compressor which includes a pair of front and rear cylinderblocks. The front cylinder block has at the center thereof a front shafthole and a plurality of front cylinder bores formed around the frontshaft hole. Similarly, the rear cylinder block has at the center thereofa rear shaft hole and a plurality of rear cylinder bores formed aroundthe rear shaft hole. The front cylinder block and the rear cylinderblock are joined together so that the front shaft hole and the frontcylinder bores are aligned with the rear shaft hole and the rearcylinder bores, respectively. The front cylinder bores and the rearcylinder bores cooperate to form a plurality of pairs of the front andrear cylinder bores. The front cylinder block and the rear cylinderblock have therebetween a swash plate chamber.

The piston compressor further includes a pair of front and rearhousings. The front housing is joined to the front cylinder block via afront valve unit including a plurality of reed type front dischargevalves and a plurality of reed type front suction valves. The fronthousing has a front discharge chamber which is communicable with thefront cylinder bores via the respective reed type discharge valves and afront suction chamber which is communicable with the front cylinderbores via the respective reed type front suction valves. Similarly, therear housing is joined to the rear cylinder block via a rear valve unitincluding a plurality of reed type rear discharge valves and a pluralityof reed type rear suction valves. The rear housing has a rear dischargechamber which is communicable with the rear cylinder bores via therespective reed type rear discharge valves and a suction chamber whichis communicable with the rear cylinder bores via the respective reedtype rear suction valves.

A drive shaft is rotatably supported at the shaft holes by the fronthousing, the front cylinder block and the rear cylinder block. A swashplate is mounted on the drive shaft for rotation therewithsynchronously. The swash plate has a boss portion held between the frontcylinder block and the rear cylinder block via thrust bearings and a camportion formed integrally with the boss portion. A plurality ofdouble-headed pistons are received in the respective pairs of front andrear cylinder bores. When the drive shaft is rotated, the cam portion ofthe swash plate causes the pistons to reciprocate in their correspondingpairs of front and rear cylinder bores. Each piston has on the oppositesides thereof in the pair of front and rear cylinder bores a frontcompression chamber and a rear compression chamber. The front cylinderblock has therein an inlet port extending radially to interconnect theswash plate chamber and the external refrigerant circuit of the pistoncompressor. The front cylinder block and the rear cylinder block havetherethrough a plurality of suction passages which extend in parallelwith the axis of the drive shaft and interconnect the front suctionchamber and the rear suction chamber via the swash plate chamber.

According to the piston compressor, the suction passage having a longerpathway from the inlet port is formed with a larger flow passage area.Thus, flow rates of refrigerant gas flowing through the suction passagesare substantially equalized and substantially the same amount ofrefrigerant gas is drawn into each compression chamber. Therefore, theintake efficiency of the compressor is improved and noise development ofthe compressor is reduced.

Some compressors dispense with reed type suction valves and instead usea rotary valve which is rotatable synchronously with the drive shaft ofthe compressor for drawing refrigerant gas selectively to the respectivecompression chambers in order to forestall a pressure loss caused by thereed type suction valves. Specifically, a compressor is known whereinrefrigerant gas in the swash plate chamber is drawn into the respectivecompression chambers not through the suction passages but throughpassages formed in the boss portion of the swash plate and also passagesformed in the drive shaft. More specifically, the boss portion of theswash plate of this compressor has therethrough a front supply port anda rear supply port which extend radially and are opened to the swashplate chamber. The supply ports are spaced from each other in rotationdirection of the swash plate. The drive shaft has therein an axial holeextending in axial direction of the drive shaft, a front guide holewhich communicates with the front supply port and the axial hole, a rearguide hole which communicates with the rear supply port and the axialhole, a front suction guide hole which communicates with the axial hole,and a rear suction guide hole which communicates with the axial hole.The front cylinder block has therein a plurality of front admissionports which are communicable with the front suction guide hole and therespective front compression chambers. The rear cylinder block hastherein a plurality of rear admission ports which are communicable withthe rear suction guide hole and the respective rear compressionchambers.

In such a compressor, refrigerant gas in the swash plate chamber isdrawn into the front and rear compression chambers through the front andrear supply ports, the front and rear guide holes, the axial hole, thefront and rear suction guide holes, and the front and rear admissionports. Thus, the front supply port, the front guide hole, the axialhole, the front suction guide hole and the front admission portscooperate to form a front suction flow passage for drawing refrigerantgas in the swash plate chamber into each front compression chamber thenon the suction stroke of the double-headed piston for the frontcompression chamber. The rear supply port, the rear guide hole, theaxial hole, the rear suction guide hole and the rear admission portscooperate to form a rear suction flow passage for drawing refrigerantgas in the swash plate chamber into each rear compression chamber thenon the suction stroke of the double-headed piston for the rearcompression chamber.

It is also required in this type of compressor that intake ofrefrigerant gas into the compression chambers should be even as in thecase of the compressor described in the aforementioned publication. Inthe above compressor wherein the supply ports are rotated in the swashplate chamber, however, the length of passage for refrigerant gas toflow from the inlet port to the supply ports is variable, so that thesame technical solution as in the case of the compressor described inthe aforementioned publication cannot be employed.

If the inlet port is formed at a position of the front or rear cylinderblock corresponding to the center of the cam portion of the swash plateas viewed in axial direction of the drive shaft, refrigerant gas drawnthrough the inlet port into the swash plate chamber tends to be diffusedby the rotation of the swash plate. Thus, intake efficiency ofrefrigerant gas flowing into the respective front and rear compressionchambers through the front and rear supply ports is reduced. In order toprevent the reduction of the intake efficiency, the inlet port is formedin one of the front and rear cylinder blocks at a position which isspaced away from, or forward or rearward of, the center of the camportion as viewed in the axial direction. An inlet port thus formed inone of the front and rear cylinder blocks is preferable from theviewpoint of prevention of refrigerant gas leakage and simple structureof the compressor, as well as the prevention of reduction of the intakeefficiency.

If the inlet port is spaced away from the center of the cam portionforward or rearward as viewed in the axial direction of the drive shaft,however, the inlet port is located close to one of the front and rearsupply ports and remote from the other. In such a case, there occursdifference in intake between the front and rear compression chambers. Inthis case, there is a fear that the temperature of refrigerant gasdischarged from the compression chambers which are lower in intakeefficiency is excessively raised and, therefore, the gasket of eitherone of the front and rear valve units deteriorates early, accordingly.Such deterioration of the gasket may badly affect the durability of thecompressor. In addition, there occurs difference in reaction forcebetween the front and rear compression chambers, thereby causingvibration which badly affects quiet operation of the compressor.

The present invention is directed to a piston compressor which offershigh durability and quiet operation while maintaining a high intakeefficiency.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a pistoncompressor includes a first cylinder block, a second cylinder block, adrive shaft, a swash plate and a plurality of double-headed pistons. Thefirst cylinder block has a first shaft hole, a plurality of firstcylinder bores and a plurality of first admission ports. The firstcylinder bores are formed around the first shaft hole and communicatewith the first shaft hole via the respective first admission ports. Thesecond cylinder block has a second shaft hole, a plurality of secondcylinder bores and a plurality of second admission ports. The secondcylinder bores are formed around the second shaft hole and communicatewith the second shaft hole via the respective second admission ports.The first cylinder block and the second cylinder block are joinedtogether. The first cylinder block and the second cylinder block form aswash plate chamber between the first cylinder bores and the secondcylinder bores. One of the first cylinder block and the second cylinderblock has therein an inlet port connected to the swash plate chamber forallowing refrigerant gas to be drawn thereinto. The drive shaft isrotatably supported at the first shaft hole and the second shaft hole bythe first cylinder block and the second cylinder block, respectively.The drive shaft has therein an axial hole, a first suction guide hole, asecond suction guide hole, a first guide hole and a second guide hole.The axial hole extends in axial direction of the drive shaft. The firstsuction guide hole communicates with the first guide hole via the axialhole and is communicable with the first admission ports of the firstcylinder block. The second suction guide hole communicates with thesecond guide hole via the axial hole and is communicable with the secondadmission ports of the second cylinder block. The swash plate is mountedon the drive shaft in the swash plate chamber for rotating therewithintegrally. The swash plate has a boss portion fitted on the drive shaftand a cam portion formed integrally with the boss portion. The bossportion has therein a first supply port and a second supply port. Thefirst supply port communicates with the first guide hole of the driveshaft and the swash plate chamber. The second supply port communicateswith the second guide hole of the drive shaft and the swash platechamber. The first supply port and the second supply port are spacedfrom each other in rotation direction of the swash plate. The pluralityof double-headed pistons are received in the respective first and secondcylinder bores and engaged with the cam portion. The rotation of the camportion of the swash plate with the drive shaft causes the double-headedpistons to reciprocate in the respective first and second cylinderbores. Opposite heads of the double-headed pistons and the first andsecond cylinder bores respectively define first compression chambers andsecond compression chambers. The first compression chamber and thesecond compression chamber are communicable with the first admissionport and the second admission port, respectively. The first supply port,the first guide hole, the axial hole, the first suction guide hole andthe first admission ports cooperate to form a first suction flow passagefor allowing the refrigerant gas in the swash plate chamber to be drawninto each first compression chamber on a suction stroke of thedouble-headed piston for the first compression chamber. The secondsupply port, the second guide hole, the axial hole, the second suctionguide hole and the second admission ports cooperate to form a secondsuction flow passage for allowing the refrigerant gas in the swash platechamber to be drawn into each second compression chamber on a suctionstroke of the double-headed piston for the second compression chamber. Adistance from the inlet port to the first supply port when the firstsupply port is moved closest to the inlet port is greater than adistance from the inlet port to the second supply port when the secondsupply port is moved closest to the inlet port. The smallest flowpassage area in the first supply port and the first guide hole isgreater than the smallest flow passage area in the second supply portand the second guide hole.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which.

FIG. 1 is a longitudinal sectional view showing a piston compressoraccording to a first embodiment of the present invention;

FIG. 2 is a fragmentary longitudinal sectional view showing the pistoncompressor of FIG. 1;

FIG. 3 is a fragmentary longitudinal sectional view showing a pistoncompressor according to a second embodiment of the present invention;

FIG. 4 is a fragmentary longitudinal sectional view showing a pistoncompressor according to a third embodiment of the present invention;

FIG. 5 is a fragmentary longitudinal sectional view showing a pistoncompressor according to a fourth embodiment of the present invention;

FIG. 6 is a fragmentary longitudinal sectional view showing a pistoncompressor according to a fifth embodiment of the present invention;

FIG. 7 is a fragmentary plan view showing front and rear cylinder boresof the piston compressor of FIG. 6;

FIG. 8 is a fragmentary plan view showing front and rear cylinder boresof a piston compressor according to a sixth embodiment of the presentinvention;

FIG. 9 is an elevation view showing a swash plate of a piston compressoraccording to a seventh embodiment of the present invention, wherein partof the swash plate is shown in cross section; and

FIG. 10 is an elevation view showing a swash plate of a pistoncompressor according to an eighth embodiment of the present invention,wherein part of the swash plate is shown in cross section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the piston compressors according to thefirst through eighth embodiments of the present invention with referenceto the accompanying drawings.

Referring to FIG. 1, the piston compressor of the first embodiment is afixed displacement type swash plate compressor. The compressor includesa front cylinder block 1 and a rear cylinder block 3. The front cylinderblock 1 has therethrough a front shaft hole 1A and a plurality of frontcylinder bores 1B formed around the front shaft hole 1A. Similarly, therear cylinder block 3 has therethrough a rear shaft hole 3A and aplurality of rear cylinder bores 3B formed around the rear shaft hole3A. The front cylinder block 1 and the rear cylinder block 3 are joinedtogether so that the front shaft hole 1A and the front cylinder bores 1Bare aligned with their corresponding rear shaft hole 3A and rearcylinder bores 3B, respectively. The front cylinder bores 1B and therear cylinder bores 3B cooperate to form a plurality of pairs of thefront and rear cylinder bores 1B and 3B. The front cylinder block 1 andthe rear cylinder block 3 have therebetween an O ring 2. The frontcylinder block 1 and the rear cylinder block 3 also have a swash platechamber 25 between the first cylinder bores 3B and the second cylinderbores 1B. It is noted that the left-hand side and the right-hand side ofFIG. 1 correspond to the front and rear of the compressor, respectively.

The compressor further includes a front housing 7 and a rear housing 11.The front housing 7 is joined to the front cylinder block 1 via a frontvalve unit 5. The front valve unit 5 includes a valve plate 51 havingtherethrough a plurality of discharge ports 51B, a plurality of reedtype discharge valves 52A which are operable to open and close thedischarge ports 51B, and a plurality of retainers 53A which restrict theopening of the discharge valves 52A. The valve plate 51 is formed on theside thereof adjacent to the front cylinder block 1 with a gasket (notshown). The gasket is formed by coating rubber material. The fronthousing 7 has therein a discharge chamber 7A which is communicable withthe front cylinder bores 1B via the respective discharge valves 52A. Thefront housing 7 and the front cylinder block 1 have therebetween an Oring 4.

In a similar manner, the rear housing 11 is joined to the rear cylinderblock 3 via a rear valve unit 9. The rear valve unit 9 includes a valveplate 91 having therethrough a plurality of discharge ports 91B, aplurality of reed type discharge valves 92A which are operable to openand close the discharge ports 91B, and a plurality of retainers 93Awhich restrict the opening of the discharge valves 92A. The valve plate91 is formed on the side thereof adjacent to the rear cylinder block 3with a gasket (not shown). The gasket is formed by coating rubbermaterial. The rear housing 11 has therein a discharge chamber 11A whichis communicable with the rear cylinder bores 3B via the respectivedischarge valves 92A. The rear housing 11 and the rear cylinder block 3have therebetween an O ring 6. The housings 7, 11 and the cylinderblocks 1, 3 are fastened together by a plurality of bolts 8 (only onebeing shown). The discharge chambers 7A, 11A communicate with a singledischarge chamber (not shown).

The front housing 7 has therethrough a front shaft hole 7B. A driveshaft 13 is rotatably supported at the shaft holes 1A, 3A and 7B by thecylinder blocks 1, 3 and the front housing 7, respectively. A swashplate 27 is mounted on the drive shaft 13 in the swash plate chamber 25for rotating therewith integrally. The swash plate 27 has a boss portion27A held between the front cylinder block 1 and the rear cylinder block3 via thrust bearings 31A, 31B and a cam portion 27B formed integrallywith the boss portion 27A. The boss portion 27A is fitted on the driveshaft 13. A plurality of double-headed pistons 17 are received in therespective pairs of the front and rear cylinder bores 1B and 3B andengaged with the cam portion 27B via a plurality of pairs of front andrear shoes 18A and 18B, respectively. When the drive shaft 13 isrotated, the cam portion 27B of the swash plate 27 causes the pistons 17to reciprocate in their corresponding pairs of front and rear cylinderbores 1B and 3B via the plurality of pairs of front and rear shoes 18Aand 18B, respectively.

The opposite heads of each piston 17 define in the pair of the front andrear cylinder bores 1B and 3B a front compression chamber 19A and a rearcompression chamber 19B. The front cylinder block 1 has therein an inletport 1C extending radially and connected to the swash plate chamber 25for allowing refrigerant gas in the external refrigerant circuit of thecompressor to be drawn into the swash plate chamber 25.

Referring to FIG. 2, the boss portion 27A of the swash plate 27 hastherethrough a front supply port 27C and a rear supply port 27D whichextend radially in opposite directions and communicate with the swashplate chamber 25. That is, the front supply port 27C and the rear supplyport 27D are spaced angularly from each other in the rotation directionof the swash plate 27 at an angle of about 180 degrees. The distancefrom the inlet port 1C to the rear supply port 27D when the rear supplyport 270 is moved closest to the inlet port 1C is greater than thedistance from the inlet port 1C to the front supply port 27C when thefront supply port 27C is moved closest to the inlet port 1C, and theflow passage area of the rear supply port 27D as viewed in cross sectionis larger than that of the front supply port 27C as viewed in crosssection. In other words, the distance from the inlet port 1C to thefront supply port 27C when the front supply port 27C is moved closest tothe inlet port 1C is shorter than the distance from the inlet port 1C tothe rear supply port 27D when the rear supply port 27D is moved closestto the inlet port 1C, and the flow passage area of the front supply port27C as viewed in cross section is smaller than that of the rear supplyport 27D as viewed in cross section. The difference in flow passage areabetween the rear supply port 27D and the front supply port 27C isdetermined so as to minimize the difference between the intake flows toeach front compression chamber 19A and to its corresponding rearcompression chamber 19B.

The drive shaft 13 has therein an axial hole 13A extending in axialdirection of the drive shaft 13, a front guide hole 13B whichcommunicates with the front supply port 27C and the axial hole 13A, arear guide hole 13C which communicates with the rear supply port 27D andthe axial hole 13A, a front suction guide hole 13D which communicateswith the axial hole 13A, and a rear suction guide hole 13E whichcommunicates with the axial hole 13A. The front guide hole 13B has thesame diameter as the front supply port 27C and the rear guide hole 13Chas the same diameter as the rear supply port 27D. That is, the distancefrom the inlet port 1C to the rear guide hole 13C when the rear guidehole 13C is moved closest to the inlet port 1C is greater than thedistance from the inlet port 1C to the front guide hole 13B when thefront guide hole 13B is moved closest to the inlet port 1C, and the flowpassage area of the rear guide hole 13C as viewed in cross section isgreater than that of the front guide hole 13B as viewed in crosssection. In other words, the distance from the inlet port 1C to thefront guide hole 13B when the front guide hole 13B is moved closest tothe inlet port 1C is shorter than the distance from the inlet port 1C tothe rear guide hole 13C when the rear guide hole 13C is moved closest tothe inlet port 1C, and the flow passage area of the front guide hole 13Bas viewed in cross section is smaller than that of the rear guide hole13C as viewed in cross section. The front suction guide hole 13D and therear suction guide hole 13E have substantially the same flow passagearea. Thus, the part of the drive shaft 13 which is located in the frontshaft hole 1A and the rear shaft hole 3A forms a rotary valve, whichimproves the intake efficiency and simplifies the structure of thecompressor.

The front cylinder block 1 has therein a plurality of front admissionports 21 which extend radially from the front shaft hole 1A and arecommunicable with the respective front compression chambers 19A. Thefront suction guide hole 13D of the drive shaft 13 is communicable witheach front admission port 21 by the rotation of the drive shaft 13. Therear cylinder block 3 has therein a plurality of rear admission port 23which extend radially from the rear shaft hole 3A and are communicablewith the respective rear compression chambers 19B. The rear suctionguide hole 13E of the drive shaft 13 is communicable with each rearadmission port 23 by the rotation of the drive shaft 13. The frontadmission port 21 and the rear admission port 23 have substantially thesame flow passage area.

Thus, the front supply port 27C, the front guide hole 13B, the axialhole 13A, the front suction guide hole 13D and the front admission ports21 cooperate to form a front suction flow passage for allowingrefrigerant gas in the swash plate chamber 25 to be drawn into eachfront compression chamber 19A then on the suction stroke of the piston17 moving rearward. The rear supply port 27D, the rear guide hole 13C,the axial hole 13A, the rear suction guide hole 13E and the rearadmission ports 23 cooperate to form a rear suction flow passage forallowing refrigerant gas in the swash plate chamber 25 to be drawn intoeach rear compression chamber 19B then on the suction stroke of thepiston 17 moving forward. In the compressor of the first embodiment, theflow passage areas of the rear supply port 27D and the rear guide hole13C are larger than those of the front supply port 27C and the frontguide hole 13B, respectively.

When the compressor of FIG. 1 is used for a vehicle air conditioner, itssingle discharge chamber (not shown) is connected to a condenser (notshown) in the external refrigerant circuit having therein othercomponents such as an expansion valve and an evaporator (each of whichis not shown) via a conduit (not shown). The evaporator is connected tothe inlet port 1C via a conduit (not shown). The drive shaft 13 isdriven by an engine (not shown) through a belt trained between theengine and a pulley or an electromagnetic clutch mounted on the driveshaft 13.

When the drive shaft 13 is driven to rotate by the engine, the swashplate 27 is integrally rotated with the drive shaft 13 thereby to causeeach piston 17 to reciprocate in its corresponding pair of front andrear cylinder bores 1B and 3B for a stroke length that is determined bythe inclination of the swash plate 27. In conjunction with thereciprocating movement of the pistons 17, fluid communication is madebetween the front suction guide hole 13D and the front admission port 21and also between the rear suction guide hole 13E and the rear admissionport 23. Thus, the swash plate chamber 25 communicates with the frontcompression chamber 19A via the front suction flow passage and also withthe rear compression chamber 19B via the rear suction flow passage.Refrigerant gas compressed in the front and rear compression chambers19A, 19B is discharged into the front and rear discharge chambers 7A,11A, respectively. Refrigerant gas discharged to the front and reardischarge chambers 7A, 11A is then delivered to the condenser via thesingle discharge chamber and the conduit and returns to the inlet port1C of the compressor via the expansion valve and the evaporator. Thus,air conditioning cycle is completed.

In the compressor, the inlet port 1C, which is formed in the frontcylinder block 1, is positioned axially forward of the center of the camportion 27B of the swash plate 27, as shown in FIG. 2, so thatrefrigerant gas is less susceptible to diffusion caused by the rotationof the swash plate 27, with the result that a high intake efficiency ismaintained. The arrangement of the inlet port 1C helps to preventrefrigerant gas from leaking and to simplify the structure of thecompressor.

In the compressor of the present embodiment wherein the flow passagearea of the rear supply port 27D is greater than that of the frontsupply port 27C, the difference between the intake flow to the frontcompression chambers 19A and the intake flow to the rear compressionchambers 19B is minimized. Accordingly, the difference in temperaturebetween the refrigerant gas discharged from the front compressionchamber 19A and from the rear compression chamber 19B is minimized, sothat early deterioration of either one of the gaskets of the valve units5 and 9 and/or of the O-rings 4 and 6 is prevented. The difference inreaction force between the front and rear compression chambers 19A and19B is also minimized, therefore, generation of vibration due to suchdifference is prevented successfully.

Consequently, the compressor of the present embodiment offers highdurability and quiet operation while maintaining a high intakeefficiency.

The piston compressor according to the second embodiment of the presentinvention will be described with reference to FIG. 3. The compressor ofthe second embodiment is substantially the same as the compressor of thefirst embodiment in that the flow passage area of the rear supply port27D of the boss portion 27A of the swash plate 27 is greater than thatof the front supply port 27C. The second embodiment differs from thefirst embodiment in that the front guide hole 13F corresponding to thefront guide hole 13B of the first embodiment has the same flow passagearea as the rear guide hole 13C. The rest of the structure of the secondembodiment is substantially the same as that of the first embodiment.

In the compressor of the second embodiment wherein the flow passage areaof the rear supply port 27D is greater than that of the front supplyport 27C, the flow resistance of refrigerant gas flowing through therear supply port 27D, which is more remote from the inlet port 1C thanthe front supply port 27C, is smaller than the flow resistance ofrefrigerant gas flowing through the front supply port 27C.

Therefore, the compressor of the second embodiment offers substantiallythe same advantageous effects as that of the first embodiment.

The piston compressor according to the third embodiment of the presentinvention will be described with reference to FIG. 4. The compressor ofthe third embodiment is substantially the same as the compressor of thefirst embodiment in that the flow passage area of the rear guide hole13C, which is more remote from the inlet port 1C than the front guidehole 13B, is greater than that of the front guide hole 13B. The thirdembodiment differs from the first embodiment in that the front supplyport 27E corresponding to the front supply port 27C of the firstembodiment has the same flow passage area as the rear supply port 27D.The rest of the structure of the third embodiment is substantially thesame as that of the first embodiment.

In the compressor of the third embodiment wherein the flow passage areaof the rear guide hole 13C is greater than that of the front guide hole13B, the flow resistance of refrigerant gas flowing through the rearguide hole 13C, which is more remote from the inlet port 10 than thefront guide hole 13B, is smaller than the flow resistance of refrigerantgas flowing through the front guide hole 13B.

Therefore, the compressor of the third embodiment offers substantiallythe same advantageous effects as that of the first embodiment.

The piston compressor according to the fourth embodiment of the presentinvention will be described with reference to FIG. 5. In the fourthembodiment, the flow passage area of the rear suction guide hole 13E,which is more remote from the inlet port 1C than the front suction guidehole 13G corresponding to the front suction guide hole 13D of the firstembodiment, is greater than that of the front suction guide hole 13G.That is, when the drive shaft 13 rotates, the shortest flow path fromthe inlet port 1C to the rear suction guide hole 13E through the firstsupply port 27D is longer than the shortest flow path from the inletport 1C to the front suction guide hole 13G through the second supplyport 27C and the flow passage area of the rear suction guide hole 13E isgreater than that of the front suction guide hole 13G. The rest of thestructure of the fourth embodiment is substantially the same as that ofthe first embodiment.

In the compressor of the fourth embodiment wherein the flow passage areaof the rear suction guide hole 13E is greater than that of the frontsuction guide hole 13G, the flow resistance of refrigerant gas flowingthrough the rear suction guide hole 13E, which is more remote from theinlet port 1C than the front suction guide hole 13G, is smaller than theflow resistance of refrigerant gas flowing through the front suctionguide hole 13G.

Therefore, the compressor of the fourth embodiment offers substantiallythe same advantageous effects as that of the first embodiment.

The piston compressor according to the fifth embodiment of the presentinvention will be described with reference to FIGS. 6 and 7. In thefifth embodiment, the flow passage area of each rear admission port 23,which is more remote from the inlet port 1C than the front admissionport 24 corresponding to the front admission port 21 of the firstembodiment, is greater than that of the front admission port 24. Eachfront admission port 24 is in the form of a round hole as viewed incross section as shown in FIG. 7 and each rear admission port 23 is alsoin the form of a round hole. The rest of the structure of the fifthembodiment is substantially the same as that of the first embodiment.

In the compressor of the fifth embodiment wherein the flow passage areaof the rear admission port 23 is greater than that of the frontadmission port 24, the flow resistance of refrigerant gas flowingthrough the rear admission port 23, which is more remote from the inletport 1C than the front admission port 24, is smaller than the flowresistance of refrigerant gas flowing through the front admission port24. The rear admission port 23 and the front admission port 24 providedby a round hole can reduce the flow resistance of refrigerant gasflowing through these admission ports 23 and 24 as compared to a casewhere the rear admission port 23 and the front admission port 24 areprovided by a hole having other shape than round shape.

Therefore, the compressor of the fifth embodiment offers substantiallythe same advantageous effects as that of the first embodiment.

In addition, there is not only the difference between the flow passagearea of the rear supply port 27D and the rear guide hole 13C and theflow passage area of the front supply port 27C and the front guide hole13B, but also the difference between the flow passage area of each rearadmission port 23 and the corresponding front admission port 24. Thus,the advantageous effects of the present invention are remarkablyaccomplished.

The piston compressor according to the sixth embodiment of the presentinvention will be described with reference to FIG. 8. In the sixthembodiment, each rear admission port 23 which is more remote from theinlet port 1C than the corresponding front admission port 26 is formedby a round hole as viewed in cross section as shown in FIG. 8. The frontadmission port 26 is formed by an elongated hole as viewed in crosssection as shown in FIG. 8. As viewed axially of the drive shaft 13, therear admission port 23 is formed with a diameter that is substantiallythe same as the length of the front admission port 26. The rest of thestructure of the sixth embodiment is substantially the same as that ofthe first embodiment.

In the compressor, the suction stroke of the piston 17 is performed atthe same timing in the front and rear compression chambers 19A and 19B,which helps to restrict the generation of vibration.

The piston compressor according to the seventh embodiment of the presentinvention will be described with reference to FIG. 9. In the seventhembodiment, the rear supply port 28 corresponding to the rear supplyport 27D of the first embodiment is formed with a projection 28A and arecess 28B. Specifically, the projection 28A is formed on the outersurface of the boss portion 27A which is formed by the trailing side ofthe opening of the first supply port 28 with respect to the rotationdirection R of the swash plate 27. The recess 28B is formed on the outersurface of the boss portion 27A which is formed by the opposite leadingside of the opening of the first supply port 28 with respect to therotation direction R of the swash plate 27. The rest of the structure ofthe seventh embodiment is substantially the same as that of the firstembodiment.

In the compressor of the seventh embodiment, during the rotation of theswash plate 27, refrigerant gas 32 can flow easily into the rear supplyport 28 that is more remote from the inlet port 1C than the front supplyport 27C.

Therefore, the compressor of the seventh embodiment offers substantiallythe same advantageous effects as that of the first embodiment.

The piston compressor according to the eighth embodiment of the presentinvention will be described with reference to FIG. 10. In the eighthembodiment, the rear supply port 30 corresponding to the rear supplyport 27D of the first embodiment is inclined from the radial directionof the boss portion 27A so as to guide the refrigerant gas 32 into theaxial hole 13A by the rotation of the swash plate 27. The rest of thestructure of the eighth embodiment is substantially the same as that ofthe first embodiment.

In the compressor of the eighth embodiment, likewise the seventhembodiment, during the rotation of the swash plate 27, refrigerant gas32 can flow easily into the rear supply port 30 that is more remote fromthe inlet port 1C than the front supply port 27C.

Thus, the compressor of the eighth embodiment offers substantially thesame advantageous effects as that of the first embodiment.

The present invention has been described in the context of theabove-described first through eighth embodiments, but it is not limitedto those embodiments. It is obvious that the invention may be practicedin various manners as exemplified below.

Although the inlet port 1C in the above-described embodiments is formedin the front cylinder block 1, the inlet port may be formed in the rearcylinder block. In this case, the above-described distant relations arereversed.

1. A piston compressor comprising: a first cylinder block having a firstshaft hole, a plurality of first cylinder bores and a plurality of firstadmission ports, wherein the first cylinder bores are formed around thefirst shaft hole and communicate with the first shaft hole via therespective first admission ports; a second cylinder block having asecond shaft hole, a plurality of second cylinder bores and a pluralityof second admission ports, wherein the second cylinder bores are formedaround the second shaft hole and communicate with the second shaft holevia the respective second admission ports, wherein the first cylinderblock and the second cylinder block are joined together, wherein thefirst cylinder block and the second cylinder block form a swash platechamber between the first cylinder bores and the second cylinder bores,wherein one of the first cylinder block and the second cylinder blockhas therein an inlet port connected to the swash plate chamber forallowing refrigerant gas to be drawn thereinto; a drive shaft rotatablysupported at the first shaft hole and the second shaft hole by the firstcylinder block and the second cylinder block, respectively, the driveshaft having therein an axial hole, a first suction guide hole, a secondsuction guide hole, a first guide hole and a second guide hole, whereinthe axial hole extends in axial direction of the drive shaft, whereinthe first suction guide hole communicates with the first guide hole viathe axial hole and is communicable with the first admission ports of thefirst cylinder block, wherein the second suction guide hole communicateswith the second guide hole via the axial hole and is communicable withthe second admission ports of the second cylinder block; a swash platemounted on the drive shaft in the swash plate chamber for rotatingtherewith integrally, wherein the swash plate has a boss portion fittedon the drive shaft and a cam portion formed integrally with the bossportion, wherein the boss portion has therein a first supply port and asecond supply port, wherein the first supply port communicates with thefirst guide hole of the drive shaft and the swash plate chamber, whereinthe second supply port communicates with the second guide hole of thedrive shaft and the swash plate chamber, wherein the first supply portand the second supply port are spaced from each other in rotationdirection of the swash plate; and a plurality of double-headed pistonsreceived in the respective first and second cylinder bores and engagedwith the cam portion, wherein the rotation of the cam portion with thedrive shaft causes the double-headed pistons to reciprocate in therespective first and second cylinder bores, wherein opposite heads ofthe double-headed pistons and the first and second cylinder boresrespectively define first compression chambers and second compressionchambers, wherein the first compression chamber and the secondcompression chamber are communicable with the first admission port andthe second admission port, respectively; wherein the first supply port,the first guide hole, the axial hole, the first suction guide hole andthe first admission ports cooperate to form a first suction flow passagefor allowing the refrigerant gas in the swash plate chamber to be drawninto each first compression chamber on a suction stroke of thedouble-headed piston for the first compression chamber, wherein thesecond supply port, the second guide hole, the axial hole, the secondsuction guide hole and the second admission ports cooperate to form asecond suction flow passage for allowing the refrigerant gas in theswash plate chamber to be drawn into each second compression chamber ona suction stroke of the double-headed piston for the second compressionchamber, and wherein a distance from the inlet port to the first supplyport when the first supply port is moved closest to the inlet port isgreater than a distance from the inlet port to the second supply portwhen the second supply port is moved closest to the inlet port, whereinthe smallest flow passage area in the first supply port and the firstguide hole is greater than the smallest flow passage area in the secondsupply port and the second guide hole.
 2. The piston compressoraccording to claim 1, wherein the respective flow passage areas of thefirst supply port and the first guide hole are greater than the flowpassage areas of the second supply port and the second guide hole. 3.The piston compressor according to claim 1, wherein the flow passagearea of the first guide hole is equal to the flow passage area of thesecond guide hole.
 4. The piston compressor according to claim 1,wherein the flow passage area of the first supply port is equal to theflow passage area of the second supply port.
 5. The piston compressoraccording to claim 1, wherein when the drive shaft rotates, the shortestflow path from the inlet port to the first suction guide hole throughthe first supply port is longer than the shortest flow path from theinlet port to the second suction guide hole through the second supplyport, and wherein flow passage area of the first suction guide hole isgreater than flow passage area of the second suction guide hole.
 6. Thepiston compressor according to claim 1, wherein when the drive shaftrotates, flow path from the inlet port to each first admission portthrough the first supply port is longer than flow path from the inletport to the corresponding second admission port through the secondsupply port, and wherein flow passage area of the first admission portis greater than flow passage area of the second admission port.
 7. Thepiston compressor according to claim 1, wherein each of the first andsecond admission ports is in the form of a round hole as viewed in crosssection.
 8. The piston compressor according to claim 1, wherein when thedrive shaft rotates, flow path from the inlet port to each firstadmission port through the first supply port is longer than flow pathfrom the inlet port to the corresponding second admission port throughthe second supply port, and wherein the first admission port is in theform of a round hole as viewed in cross section and the second admissionport is in the form of an elongated hole as viewed in cross section. 9.The piston compressor according to claim 1, wherein a projection isformed on the outer surface of the boss portion which is formed by atrailing side of the opening of the first supply port with respect tothe rotation direction of the swash plate.
 10. The piston compressoraccording to claim 1, wherein the first supply port is inclined fromradial direction of the boss portion so as to guide the refrigerant gasinto the axial hole by the rotation of the swash plate.